Autoantibodies are universally found in patients suffering from systemic lupus erythematosus. The presence of these antibodies has led investigators to conclude that SLE is an autoimmune disease. In some clinical settings powerful evidence supports the conclusion that specific autoantibodies induce tissue injury and are responsible for clinical manifestations. Anti-Sm and anti-nRNP autoantibodies are commonly found at extraordinary concentrations in the sera of lupus patients. When these autoantibodies are found concomitantly they are associated with renal disease and a poor disease prognosis. Anti-nRNP autoantibodies in the absence of Sin are associated with a more limited form of lupus. Anti-nRNP is also associated with other autoimmune diseases, such as mixed connective tissue disease, Raynaud's phenomenon, scleroderma and myositis. This proposal sets forth to explain the development of anti-spliceosomal autoimmunity. Through our previous work studying the fine specificity of autoantibodies binding to the spliceosome, we have identified over 150 peptide epitopes, 40 of which tend to be shared among patients. We have found that the fine specificity progresses from a small number to as many as 86 different antigenic regions for an individual patient over time. Patients with anti-Sm antibodies appear to initially bind the structure defined by PPPGMRPP. This response evolves by epitope spreading to other structures of the antigen. Immunization with this peptide has led to a novel model of lupus complete with spliceosomal autoimmunity, anti-double-stranded DNA antibodies, renal disease, thrombocytopenia, and seizures. Immunization with the closely related PPPGRRP sequence, which is found in a virus and which crossreacts with Sm, also induces anti-spliceosomal autoimmunity. We request the resources to identify the initial target epitopes of anti-nRNP autoantibodies in SLE sera. We will confirm that PPPGMRPP, as well as the first epitopes of anti-nRNP, are indeed the first epitope(s) of the anti-spliceosomal response. We will utilize a largely untapped resource allowing analysis of humoral events prior to SLE diagnosis (see Project 1). We will find peptides from the environment (especially from microorganisms) which are similar to the initial target epitopes and will determine if the initial target peptide epitopes from the spliceosome (and their structurally similar peptides from the environment) are cross-reacting antigens. We will also determine whether the peptides from the spliceosome or environment induce lupus autoimmunity after peptide immunization.